1. Field of the Invention
The present invention relates to a pseudo deep bass generating device which causes users to pseudoly perceive a bass sound in a band which is difficult for speakers to reproduce.
2. Description of Related Art
In recent years, there has been a tendency to place importance on housing design for a liquid crystal DTV and the like, and a slimmed liquid crystal DTV and the like have been accepted.
Therefore, there has been a tendency to downsize speakers mounted in a liquid crystal DTV or the like, it becomes difficult to provide an adequate feeling of a bass sound according to the downsizing.
A technology of using “Missing fundamental” which is one of psychoacoustics features is known as a technology of providing a feeling of a bass sound.
“Missing fundamental” is a feature of making a user hear two or more sounds of different frequencies simultaneously in such a way that users can have an illusion that he or she hears a sound having a frequency which is the difference between them.
A pseudo deep bass generating device which uses “Missing fundamental” is disclosed by the following patent reference 1.
This pseudo deep bass generating device generates a harmonic component signal from a low frequency component signal having a frequency equal to or lower than the lowest reproduction frequency f0 of a speaker, and adds the harmonic component signal to the original signal.
More specifically, the pseudo deep bass generating device generates an odd-order harmonic component signal by peak-holding the low frequency component signal having a frequency equal to or lower than the lowest reproduction frequency f0 of the speaker, and also generates an even-order harmonic component signal by half-wave-rectifying the odd-order harmonic component signal.
In the generation of the odd-order harmonic component signal with the peak holding, a sampled value to be outputted is determined by comparing an immediately previous sampled value with a current sampled value.
For example, in a case in which the current sampled value is positive, the output value is the immediately previous sampled value if the current sampled value is smaller than the immediately previous sampled value, whereas if the current sampled value is larger than the immediately previous sampled value, the output value is the current sampled value.
In contrast, in a case in which the current sampled value is negative, the output value is the immediately previous sampled value if the current sampled value is larger than the immediately previous sampled value, whereas if the current sampled value is smaller than the immediately previous sampled value, the output value is the current sampled value.
Therefore, when the sign of the sampled value is inverted, a discontinuous point appears. This results in a rapid change in the amplitude value, and therefore the stability may be lost from the sound and the sound quality may degrade.
FIG. 14 is an explanatory drawing showing an example of the generation of the odd-order harmonic component signal with the peak holding in the form of time waveforms. A time waveform on the left side of FIG. 14 shows a sine wave of 50 Hz, and a time waveform on the right side of FIG. 14 shows the odd-order harmonic component signal generated with the peak holding.
As can be seen from FIG. 14, because when the sign of the sampled value is inverted, the signal becomes discontinuous and hence the amplitude value varies rapidly, the sound quality degrades.
[Patent reference 1] JP,2005-318598,A (see paragraph numbers [0024]to [0032] and FIG. 1)
Because the conventional pseudo deep bass generating device is constructed as mentioned above, the conventional pseudo deep bass generating device can cause users to pseudoly perceive a bass sound in a band which is difficult for speakers to reproduce by peak-holding a low frequency component signal to generate an odd-order harmonic component signal, and then adding the odd-order harmonic component signal to the original signal. However, in the case of generating the odd-order harmonic component signal by peak-holding the low frequency component signal, the odd-order harmonic component signal becomes discontinuous when the sign of the low frequency component signal is inverted. Therefore, a problem is that a rapid change in the amplitude value causes degradation in the sound quality.